You probably have a sticking control valve. (MAKE SURE ENGINE IS OFF)Open the right side acess cover and you'll see an "H" shaped contol fork hanging down. Reach down into the fluid and feel for the "T" shaped control valve stem that is in a the sockets at the end of the control fork. Push forward and then pull back.the valve should move freely in and out about an inch.. Now start it up, making ure the pto is engaged since it runs the hydraulic pump. (UNDER NO CIRCUMSTANCES PLACE YOU HAND INTO THE HYDRAULIC COMPARTMENT WITH THE ENGINE RUNNING.) Excercise the lift lever up and down and watch the contol fork move the control valve foward (RAISE) and rearward (LOWER). If it's working that way, drain the fluid out, flush the sump with some diesel from a tank sprayer and drain it out. Sop up and remove any crud remaining in the sump and fill with fresh UTF. It will take 6 gallons.